I had Jun supply the parts for my race engine, it has all of what is in yours plus a few more things (Bigvalves, block, Gt cooling, Head, etc), they recommended a modified N1 block (there is oiling problems on number 6) or GT block, and a harmonic damper if reving over 8,300 RPM
What have you done to the block?, if it is stock it will crack on number 4 water gallery much over 600hp at the engine
Also have you balanced your Jun crank? when ours was delivered we done a full rebalance on all the components and found the crank balance needed to be adjusted
here is engine pic